<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<title></title>
	<link rel="stylesheet" href="">
	<style type="text/css">
		.box1{
			width: 500px;
			height: 500px;
			padding: 50px;
			background: red;
			/* 让边框属于盒子的内部 */
			box-sizing: border-box;
		}
	</style>
</head>
<body>
	<div class="box1"></div>
</body>
</html>